Step switch for operation of four load switching contacts for regulating transformers



June 8, 1965 K BUHLER 3,188,402

STEP SWITCH FOR OPEIATION OF FOUR LOAD SWITCHING CONTACTS FOR REGULATING TRANSFORMERS Filed Sept. 7, 1961 V 2 Sheets-Sheet l INVENTOR. Kar L B 0' h er J MJWZOPMAW June 8, 1965 K BUHLER 3,188,402

STEP SWITCH FOR OPER ATION OF FOUR LOAD SWITCHING CONTACTS FOR REGULATING TRANSFORMERS Filed Sept. 7, 1961 2 Sheets-Sheet 2 oc |so'- 24o l E] El 16 W2 1 EU- U "3 W3 Fig 3 INVENTOR. 'KOJL BOA/er BY WM 6 2 PJEW United States Patent "cc 3,188,402 STEP SWITCH FOR OPERATION OF FOUR LOAD SWITCHING CONTACTS FOR REGULATING TRANSFORMERS Karl Biihler, Nussbaumen, Aargau, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Filed Sept. 7, 1961, Ser. No. 136,500 Claims priority, application Switzerland, Sept. 7, 1960, 10,125/60 3 Claims. (Cl. 200-4) This invention relates to electrical switches and more particularly to an improved construction for a stepping switch for actuating four load switching or tap changing contacts of a regulating transformer.

The improved construction provides a driving crank rod of a crank gear for each of the four switching points arranged such that closing of the contacts at each switching point occurs only when the driving rod occupies its extreme outermost position, that the length of the driving rod is less than six fold the crank radius, that the angle of crank rotation for the contact movement is limited, being greater than 150 and less than 240 and that the cranks are mutually displaced for /3 of the angle of rotation of the crank in each case.

The improved construction according to the invention will become more clearly understood from the following detailed description of a preferred embodiment thereof and from the accompanying drawings wherein:

FIQ. 1 shows the switch partly in elevation and partly in section;

FIG. 2 is a family of curves showing the progress of the switch contact motion; and

FIG. 3 shows the complete switch with circuit connectron from the four sets of switching contacts and other circuit components.

With reference now to FIG. 1, it will be seen that the four switch units 1, 2, 3 and 4 are arranged in a cruciform configuration. Each switch unit includes a housing which forms a quenching chamber for the contact members housed therein. The quenching chamber for switch unit 2 is shown in longitudinal central section and is representative of the switch construction for the other three switch units which therefore have been illustrated in elevation only. With reference to the switch unit 2, it will L be seen that the quenching chamber encloses a pair of switch contacts 2a, 2b. Switch contact 2a is generally stationary but is yieldingly mounted on a spring so as to be able to give slightly as the movable contact 2h comes into engagement therewith. Contact member 2b has a cylindrical configuration and is hollow so as to form a nozzle and includes a piston portion which operates in a guide cylinder 2c. Contact member 2b is shown in the position drawn away from the stationary contact member 2a. The quenching housings for the four switch units 14 are fastened in place to the respective sides of a squarely configured cylinder block 50.

The driving or crank rods for actuating the piston portions of the movable contact members are designated a, a, a and a. Crank rod 20a is connected to its associated contact piston by means of a pivot bearing 2d and the other crank rods are similarly connected to their contact pistons. In accordance with the invention, closure between the stationary and movable contact members of any of the switch units takes place only when the associated crank rod occupies its extreme outer position. That is to say when the axis of the crank rod is aligned with the piston axis, as indicated by the position of crank rod 10a. In all other positions of the crank rods, the contact members of each switch unit are separated. Also, the length of the crank rod is kept as small as possible 3,188,402 Patented June 8, 1965 and in any case is maintained smaller than six fold the radius 1' which is shown on the drawing and is the crank radius. This is the radius of the circular path along which the inner end of the crank rod moves. Advantageously a multiple 3 or 4 of the crank radius is selected for the length of the crank rods. Motion of the movable contact members of the several switch units is thereby determined by the course of the angle a of crank rotation. This angle of crank rotation is limited to a range between more than and less than 240. For rotating the crank rods it will be seen that their inner ends are connected by crank pin bearings 10c, 20c, 30c and 400 on crank plates 10d, 20d, 30d and 4011' which are driven in rotation by means of spur gears 10b, 20b, 30b, and 40b mounted eccentrically thereon. The spur gears mesh with a larger spur gear 15 which is mounted concentrically on a hollow shaft 16 to which rotation is imparted by the force accumulator which has not been illustrated. The meshing of the smaller spur gears 10b, 20b, 30b and 40b with the larger spur gear 15 is such that the crank rods are mutually displaced for /3 of the total angle at of crank rotation. Since this angle is more than 150 and less than 240 it will be obvious that rotation of the driving gear 15 is not continuous in one direction but rather is oscillatory.

The construction of the gearing and the crank rods makes it feasible to obtain a most rapid movement of the movable contact members of each switch unit in the vicinity of the stationary contact member, i.e. when touching of the contacts is just about to take place. The contact movement is decelerated when movable contact is in the vicinity of its maximum distance from the associated stationary contact. The result is that the movable contacts when in the full separated position obtain quickly a relative large contact spacing.

Movement of the switch contact members in relation to movement of the driving spur gear 15 is illustrated graphically in FIG. 2. There it will be seen that the maximum movement a of a crank rod which can exist within the range of 150 to 240 serves as the movement scale. Curves K1, K2, K3 and K4 show the movements of the individual movable contact members relative to their associated stationary contact members. The periodic positions of the contact closures differ by /3oc, %a and %a, respectively. The contact members of each switch unit are closed within the range G while they are open within the range F. The curves of movement present a distorted sine wave with a lag in positions of contact closure. The effect of this distortion is that the transition from a contact closed state to a contact open state is performed quickly and that the contact members attain a relatively large spacing therebetween within a. wide aperture range. Thus a maximum protection against spark-over between the contact members is obtained.

Referring now to FIG. 3, it will be seen that a shortcircuit contact arm 25 is secured to the hollow shaft 16 so as to be rotated therewith for additional shunting and disconnection of the load contacts after switching. When shaft 16 and hence contact arm 25 rotates clockwise as viewed in FIG. 3 it makes engagement with a stationary contact member 26 after actuation of all the load switching contacts. Conversely when contact arm 25 reverses its direction of rotation it makes engagement with stationary contact member 27.

The contacts of the switch units 2 and 3 are connected through resistance elements W2 and W3 respectively with selector contacts 28, 29 respectively of the transformer step switch, it being noted that contact 28 is connected to contact 26 and contact 29 connected to contact 27. The improved step switch construction makes it possible to perform the actuation of the four load switching con- U tacts in an extremely short time, i.e. less than of a second. It is also feasible to construct the switch in a very limited space so that it is particularly well suited for attachment to the outside of the oil tank of the power transformer or for location within the tank itself.

I claim:

1. In an electrical switching device for actuating a plurality of sets of load switching contacts of a regulating transformer in a sequential manner, the combination comprising a main driving spur gear mounted for rotation about its axis, a contact operating spur gear for each set of load switching contacts, said contact operating spur gears being meshed with and arranged in spaced relation about the periphery :of said main spur gear, a crank plate mounted 'on each of said contact operating spur gears, a crank rod for each of said crank plates and having one end thereof connected on said crank plate by an articulated joint for rotation about the axis of the contact operating spur gear, a piston connected to the opposite end of each said crank rod by an articulated joint, and a stationary guide cylinder for and receiving each said piston, each said set of load switching contacts being constituted by a stationary contact mounted internally of the guide cylinder correlated thereto and a movable contact mounted on the head of the piston operating therein, said sets of movable and stationary contacts being actuated in sequence by rotation of said main spur gear and being closed only when said crank rods and pistons occupy essentially their outermost position, the length of each said crank rod being greater than it but less than 611 wherein it constitutes the radius of crank rotation, and movement of said contacts between their full open and closed positions is efiected with an angle of crank rotation between 150 and 240 degrees.

2. An electrical switching device as defined in claim 1 wherein the length of each said crank rod is between 3n and 4n.

d. An electrical switching device as defined in claim 1 wherein four of said sets of load switching contacts are provided and the four guide cylinders correlated respectively therewith are arranged apart about a center coincident with the center of said main spur gear.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. 

1. IN AN ELECTRICAL SWITCHING DEVICE FOR ACTUATING A PLURALITY OF SETS OF LOAD SWITCHING CONTACTS OF A REGULATING TRANSFORMER IN A SEQUENTIAL MANNER, THE COMBINATION COMPRISING A MAIN DRIVING SPUR GEAR MOUNTEDC FOR ROTATION ABOUT ITS AXIS, A CONTACT OPERATING SPUR GEAR FOR EACH SET OF LOAD SWITCHING CONTACTS, SAID CONTACT OPERATING SPUR GEARS BEING MESHED WITH AND ARRANGED IN SPACED RELATION ABOUT THE PERIPHERY OF SAID MAIN SPUR GEAR, A CRANK PLATE MOUNTED ON EACH OF SAID MAIN SPUR GEAR, A SPUR GEARS, A CRANK ROD FOR EACH OF SAID CRANK PLATES AND HAVING ONE END THEREOF CONNECTED ON SAID CRANK PLATE BY AN ARTICULATED JOINT FOR ROTATION ABOUT THE AXIS OF THE CONTACT OPERATING SPUR GEAR, A PISTON CONNECTED TO THE OPPOSITE END OF EACH SAID CRANK ROD BY AN ARTICULATED JOINT, AND A STATIONARY GUIDE CYLINDER FOR AND RECEIVING EACH SAID PISTON, EACH SAID SET OF LOAD SWITCHING CONTACTS BEING CONSTITUTED BY A STATIONARY CONTACT MOUNTED INTERNALLY OF THE GUIDE CYLINDER CORRELATED THERETO AND A MOVABLE CONTACT MOUNTED ON THE HEAD OF THE PISTON OPERATING THEREIN, SAID SETS OF MOVABLE AND STATIONARY CONTACTS BEING ACTUATED IN SEQQUENCE BY ROTATION OF SAID MAIN SPUR GEAR AND BEING CLOSED ONLY WHEN SAID CRANK RODS AND PISTONS OCCUPY ESSENTIALLY THEIR OUTERMOST POSITION, THE LENGTH OF EACH SAID CRANK ROD BEING GREATER THAN N BUT LESS THAN 6N WHEREIN N CONSTITUTES THE RADIUS OF CRANK ROTATION, AND MOVEMENT OF SAID CONTACTS BETWEEN THEIR FULL OPEN AND CLOSED POSITIONS IS EFFECTED WITH AN ANGLE OF CRANK ROTATION BETWEEN 150 AND 240 DEGREES. 